Digital-to-Analog converters (DACs) are found in many electronic devices. For example, DACs are used in PDAs (Personal Digital Assistant), cellular phones, computers, video players and CD players. DACs convert a digital signal into an analog signal. Analog signals include music and voice.
In the process of converting a digital signal to an analog signal, noise may be created. Noise may be any electrical contribution added to a signal that was not part of the original source that created the signal. For example, some sources of noise are thermal noise, phase noise, quantization noise and switching noise. During the process of converting a digital signal to an analog signal, the original signal may be distorted. There are many types of distortion such a harmonic distortion, and intermodulation distortion.
At low signal levels, the human ear is very sensitive to low level noise and distortion. Because the human ear is very sensitive to noise and distortion at low signal levels, methods have been devised to attenuate noise and distortion at low signal levels. For example, noise-shaping filters shift quantization noise from in-band (typically from 20 Hz to 20,000 Khz, the frequency range of human hearing) to out-of-band quantization noise (typically from 20 KHz and above). AFIR (Analog Finite Impulse Response) filters are used to reduce out-of-band noise (OBN).
Due to manufacturing variance, current segments in a DAC array will have slightly different values from each other. This variance in the current segments of a DAC array may cause harmonic distortion and may raise the noise level in a DAC. Inter-symbol interference due to uneven rise and fall times and parasitic capacitances may cause distortion and noise as well.